Modeling Default Data Via an Interactive Hidden Markov Model

In this paper, we first introduce the use of an interactive hidden Markov model (IHMM) for modeling and analyzing default data in a sector. Under the IHMM, transitions of the hidden risk states of the sector depend on the observed number of bonds in the sector that default in the current time period. This incorporates the feedback effect of the number of defaults on the transitions of the hidden risk states. This feature seems to be more realistic and does not enjoy by the traditional HMMs. We then develop a “dynamic” version of the binomial expansion technique (BET) modulated by the IHMM for modeling the occurrence of defaults of bonds issued by firms in the same sector. Under the BET modulated by the IHMM, the number of bonds defaulting in each time period follows a Markov-modulated binomial distribution with the probability of defaulting of each bond depending on the states of the IHMM, which represent the hidden risk states of the sector. Efficient method will be presented for estimating the model parameters in the BET modulated by the IHMM. We shall compare the hidden risk state process extracted from the IHMM-modulated BET with that extracted from the BET modulated by HMM in order to illustrate the significance of the feedback effect using real data. We shall also present the estimation results for the BET modulated by the IHMM and compare them with those for the BET modulated by the HMM.     

Morphology,Electrical, and Rheological Properties of Silane‐Modified Silver Nanowire/Polymer Composites

Electrically conducting films containing AgNws, hydrophilic and hydrophobic resins were prepared. FT‐IR reveals that the interface between the AgNws and epoxy could be successfully modified by APTES. XPS shows that the AgNws were attracted by hydrogen bonds of ? NH₂ and ? NH? groups after APTES modification. SEM analysis shows that the AgNws were well dispersed in the resin. The AgNws were also blended with hydrophilic and acrylic resins, and the resulting blends were compared with AgNws/epoxy blends. Results show that AgNw/PVA‐resin films possess the lowest surface electrical resistance. The AgNw/PVA‐resin and silane‐modified AgNw/epoxy resin conductive films possess a similar electrical percolation threshold.

     

The challenge of the codification of tacit knowledge in designing and making: a case study of CAD systems in the Hong Kong jewellery industry

Using the separation of designing and making activities in quantity-production systems of the Hong Kong jewellery industry as a case, this paper will show that codifying the tacit knowledge into the CAD systems is becoming deliberately feasible when the tacit knowledge are converted into accessible and applicable formats without losing its distinctive properties. The contextual analysis of the conventional jewellery production systems indicates that the separation of knowledge leads the consequence and the problems of partial representation. In order to study how the tacit-format attributes, which were separately contributed by the jewellery designers and goldsmith, can be extracted, recaptured, recorded, integrated and finally coded into CAD database, a project of scanning a hand-crafted 3D object was initiated and implemented. The successful result of the tested project not only demonstrates the feasibility of codification of tacit knowledge in design representation, but also gives a strong theoretical foundation of the extendibility of both tacit and coded knowledge in a design perspective.     

Single-switch electronic ballast with near-unity power factor andsoft-switching characteristic

The design and analysis of a single-switch electronic ballast with near-unity power factor and soft-switching characteristic are presented. The ballast circuit is simple and has a small component count. The experimental results for an 80 W ballast show that it has a power factor higher than 0.99 and a total harmonic distortion of 12%. The operating frequency is between 20-40 kHz. The output power is adjustable and the circuit is reliable     

Image restoration by regularisation in uncorrelated transformdomain

Conventional spatially adaptive regularised image restoration schemes weight the amount of regularisation according to the spatial content of an image. The authors first separately decorrelate the signals under analysis into uncorrelated components and then weight the amount of regularisation performed to these components accordingly. The proposed approach works better than conventional schemes, especially in edge regions     

Structural investigation and improvement of photoluminescence properties in Ba(ZrxTi1−x)O3 powders synthesized by the solid state reaction method

In this paper, Ba(Zr_xTi_1−x)O₃ powders with different (x) compositions were synthesized by the solid state reaction method and their structure and improvement of photoluminescence (PL) properties with the Ti substitution by Zr were discussed. The structural investigation of these powders was performed by means of X-ray diffraction (XRD) and Fourier transform Raman (FT-Raman) spectroscopy. Their optical properties were monitored by ultraviolet–visible (UV–vis) absorption spectroscopy and PL measurements. XRD patterns indicated that the powders with x = 0 and 0.1 have a tetragonal structure while compositions with x ≥ 0.2 exhibit cubic structure. FT-Raman spectra revealed that the replacement of Ti by Zr significantly reduced the intensity of the Raman active modes. This behavior is related to the increase of undistorted [ZrO₆] clusters in the global matrix at short range and decrease in local concentration of distorted octahedral [TiO₆] clusters. UV–vis absorption spectra shown the presence of intermediary energy levels between the valence band (VB) and the conduction band (BC). These intermediary electronic levels are mainly related to 2p orbitals of O atoms, 4d orbitals of Zr atoms and 3d orbitals of Ti atoms between the VB and CB. A significant improvement in PL properties of Ba(Zr_xTi_1−x)O₃ powders was observed with an increase of undistorted [ZrO₆] clusters in the lattice. Finally, we propose possible wideband models based on intermediary energy deep and shallow levels to explain the PL behavior at room temperature.     

Detection of lead in water using laser-induced breakdown spectroscopy and laser-induced fluorescence

Laser-induced breakdown spectroscopy (LIBS) is a well-known technique for fast, stand-off, and nondestructive analysis of the elemental composition of a sample. We have been investigating micro-LIBS for the past few years and demonstrating its application to microanalysis of surfaces. Recently, we have integrated micro-LIBS with laser-induced fluorescence (LIF), and this combination, laser ablation laser-induced fluorescence (LA-LIF), allows one to achieve much higher sensitivity than traditional LIBS. In this study, we use a 170 microJ laser pulse to ablate a liquid sample in order to measure the lead content. The plasma created was re-excited by a 10 microJ laser pulse tuned to one of the lead resonant lines. Upon optimization, the 3sigma limit of detection was found to be 35 +/- 7 ppb, which is close to the EPA standard for the level of lead allowed in drinking water.     

SSOR preconditioned CG method for the linear interference cancellation of asynchronous CDMA systems

An ideal computation of the decorrelating or the linear minimum mean-squared-error (LMMSE) detector requires computational complexity of order K ³ when there K is the number of users. To alleviate the computational complexity, iterative decorrelating and LMMSE detectors are proposed for solving a set of linear equations corresponding to linear interference cancellation structures. Iterative conjugate gradient (CG) method has been used for the linear interference cancellation detectors. Its main advantages are to reduce the order of computation complexity and their suitability to highly parallel implementations. In this paper, the symmetric successive overrelaxation (SSOR) preconditioning scheme is applied to the CG method. The performance of the detectors is investigated and it is found that the SSOR preconditioned CG method can provide significantly faster convergence than CG method.